A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to make use of a lithographic apparatus as efficiently as possible, it is desirable to achieve a high throughput of the lithographic apparatus, so that a large amount of substrates can be processed by the lithographic apparatus in the short time.
In a scanning mode of a scanning-type lithographic apparatus, the substrate table is moved with a substrate table scanning movement, i.e. a movement with a substantially constant speed, across a projection system. At the same time as the scanning movement of the substrate table, a support supporting a patterning device is scanned also with a scanning movement, i.e. a movement with substantially constant speed across the projection system to impart a pattern in a radiation beam of the lithographic apparatus. Since, during projection, the support of the patterning device is moved from a starting position to an end position, the patterning device support has to be moved back to the start position before the patterning device support is ready for a new scanning movement in the same direction.
Therefore, the lithographic apparatus may be configured to make a meandering pattern of substrate table scanning movements over the substrate. The subsequent scanning movements of the patterning device support may then be in opposite directions, since the direction of the subsequent substrate scanning movements is also in opposite directions. For each substrate table scanning movement, the substrate table has to be decelerated and accelerated to obtain the desired speed and direction. Such deceleration and subsequent acceleration to a substantially constant speed takes considerable time.
During this time for deceleration and acceleration, the lithographic apparatus can not be used for the exposure of image fields on the substrate, which has a negative influence on the throughput of the lithographic apparatus. Since there is an increasing need to increase throughput of a lithographic apparatus, it is desirable that the exposure of target portion a substrate can be performed more efficiently.
A possible solution would be to use of larger reticles which may comprise a number of image fields to expose multiple target portions on the substrate. However, in practice, the possibilities for substantially increasing the size of reticles, while maintaining the same specifications of the reticle are limited.